Method of making moisture resistant aluminum nitride powder and powder produced thereby

Abstract

A method for making a moisture-resistant aluminum nitride-containing powder which includes (a) coating a layer of silicate onto aluminum nitride-containing powder having aluminum nitride on at least a portion of its surface and (b) heat-treating the coated aluminum nitride-containing powder at a temperature of from 350° to 1000° C. for a period of time sufficient to cause the silicate to react with the surface aluminum nitride thereby forming a layer of Si--Al--O--N bonded to the surface aluminum nitride. The silicate has alkyl or alkoxyalkyl radicals attached thereto. The method yields a moisture-resistant aluminum nitride-containing powder having a layer of Si--Al--O--N reaction-bonded to the surface aluminum nitride.

We claim: 
     
       1. A method for making a moisture-resistant aluminum nitride-containing powder, comprising: (a) oxidizing an aluminum nitride-containing powder by contacting with an oxygen containing atmosphere at elevated temperatures,   (b) coating a layer of a silicate onto said aluminum nitride-containing powder having aluminum nitride on at least a portion of its surface, the silicate having substituents thereon selected from the group consisting of alkyl and alkoxyalkyl radicals, and   (c) heat-treating the coated aluminum nitride-containing powder at a temperature of from 350° to 1000° C. for a period of time sufficient to cause the silicate to react with the surface aluminum nitride thereby forming treated aluminum nitride-containing powder having a layer of Si--Al--O--N bonded to the surface aluminum nitride.   
     
     
       2. The method of claim 1, wherein the silicate has the following general structure:   RO({RO}.sub.2 SiO).sub.n Si(OR).sub.3     wherein each R is independently selected from the group consisting of alkyl and alkoxyalkyl radicals, the alkyl and alkoxyalkyl radicals having from 1 to 12 carbon atoms, inclusive, and n is a number from zero to 2, inclusive.   
     
     
       3. The method of claim 1, wherein the heat-treating step is performed at a temperature of from 500° to 700° C. 
     
     
       4. The method of claim 1, wherein the heat-treating step is performed for a period from 1 hour to 2 hours. 
     
     
       5. The method of claim 1 wherein the coating step is performed by applying a solution of the silicate and a solvent onto the aluminum nitride-containing powder, and the method further comprises removing the solvent from the coating and exposing the powder to a temperature in the range of 75° C. to 200° C. before heat-treating the coated aluminum nitride-containing powder. 
     
     
       6. The method of claim 5 wherein the powder is exposed to a temperature in the range of 100° C. to 150° C. before heat-treating the coated aluminum nitride-containing powder. 
     
     
       7. The method of claim 1, further comprising: (d) coating a layer of a second silicate onto the treated aluminum nitride-containing powder, the second silicate having substituents thereon selected from the group consisting of alkyl and alkoxyalkyl radicals, and   (e) heat-treating the coated treated aluminum nitride-containing powder at a temperature of from 350° to 1000° C. for a period of time sufficient to cause the second silicate to form an amorphous layer containing Si and O on the treated aluminum nitride-containing powder.   
     
     
       8. The method of claim 1, wherein the coating step is performed by (a) dispersing the aluminum nitride-containing powder in an alkyl alcohol having from 1 to 4 carbon atoms, inclusive, to form a dispersion, and   (b) dissolving into the dispersion, in the following order: (i) the silicate and   (ii) water.     
     
     
       9. The method of claim 8, wherein a hydrolysis catalyst is dissolved into the dispersion after the water. 
     
     
       10. The method of claim 9, wherein, in the coating solution, the alkyl alcohol is employed in an amount from 50 to 300 volume percent based on the volume of the aluminum nitride-containing powder,   the silicate is employed in an amount from 1 to 150 weight percent based on the weight of the aluminum nitride-containing powder,   the water is employed in an amount from 100 to 400 weight percent based on the weight of the silicate, and   the hydrolysis catalyst is employed in an amount from 10 to 75 weight percent based on the weight of the water.   
     
     
       11. The method of claim 1, wherein the silicate is employed in an amount from about 5 to about 50 weight percent based on the weight of the aluminum nitride-containing powder and the water is employed in an amount from about 100 to about 200 weight percent based on the weight of the silicate.